A permanent magnet type linear pulse motor in this field is disclosed in, for instance, in FIG. 6 of Japanese Patent Laid-Open No. 56-74080 published on June 19, 1981 in the title of "Linear pulse motor", in which a stator provided with a permanent magnet and a mover wound coils to a magnetic pole having teeth are opposed each other.
However, the prior art has a drawback in that a friction force is generated between wheels for sliding a mover on a stator through the wheels and the stator, and vibration along a perpendicular direction of the mover is increased when a magnetic pull force generated between the stator and the mover is increased.
FIG. 1 shows a main structure of the permanent magnet type linear pulse motor of the prior art. On the stator yoke 3 in FIG. 1, a permanent magnet 4 is provided. The permanent magnet 4 arranges N pole and S pole alternatively on the stator yoke 3. The pitches of N pole and S pole on the stator yoke 3 are same to that of the movers 1 and 2. The movers 1 and 2 are wound by coils 6 and 7, respectively. The teeth of the movers 1 and 2 are arranged to have a delay of T/2 pitch, respectively, to the magnetic pitch T of the permanent magnet 4 of the stator yoke 3. The movers 1 and 2 are connected by a non-magnetic material 8. The direction and the strength of the magnetic pull force applied between the stator and the mover is changed relating to the opposed position between the teeth of the movers 1, 2 and the permanent magnet 4. In the opposed position shown in FIG. 1, magnetic fluxes shown by arrows are generated at the space between the teeth of the movers 1, 2, and the permanent magnet 4. When current flows to the coil 7 generating the flux .PHI..sub.c, the magnetic flux 41 generated from the N pole of the permanent magnet 4 to the tooth of the magnetic pole 21 declining to the left as shown by the arrow is increased. The magnetic flux 42 generated from the tooth of the magnetic pole 21 to the S pole of the permanent magnet 4 declining to the right as shown by the arrow is counterbalanced by the flux .PHI..sub.c and is decreased thereby. In the space between the magnetic pole 22 and the permanent magnet 4, the magnetic flux 44 generated from the tooth of the magnetic pole 22 to the S pole of the permanent magnet 4 declining to the right is increased, and the flux 45 generated from the N pole of the permanent magnet 4 to the tooth of the magnetic pole 22 is decreased. As a result, the magnetic pull force of the stator 3 to the mover 2 is unbalanced, the thrust force directed to the right is generated at the stator 3 to the mover 2 so that the movers 1 and 2 are moved to the right. Incidentally, when current flows to the coil 6 of the mover 1 at the positional relationship shown in FIG. 1, no magnetic pull force to the mover 1 is generated to either left or right direction along the surface of the stator 3 so that thrust force is not generated between the mover 1 and the stator 3. Namely, when the teeth of the mover 1 or 2 has a delay of T/2 pitch, respectively, to the magnetic pitch T of the permanent magnet 3 of the stator yoke 3, the maximum thrust force is generated.
FIG. 2 illustrates a thrust force wave diagram of the prior linear pulse motor to the position x of the mover. When a constant current is flowed to the coils 6 and 7, the thrust force shown by the dotted line in (a) of FIG. 2 is generated to the mover 1, and the thrust force shown by the dotted line in (b) of FIG. 2 is generated to the mover 2. When the positional relationship between the movers 1, 2, and the stator 4 is as shown in FIG. 1, the position X of the mover in FIG. 2 corresponds to the reference point 0 thereat. Namely, when the direction of current flowing through the coils 6, 7 is changed over at each 1/2 period of the tooth pitch T of the movers 1 and 2, one directional thrust force is generated as shown by the solid line in (a) and (b) of FIG. 2, so that the linear pulse motor shown in FIG. 1 performs a linear motion.
FIG. 3 shows a relationship between the position X of the mover and the magnetic pull force f.sub.p. In FIG. 3, (a) and (b) correspond to the characteristic of the movers 1 and 2, respectively. The pure magnetic pull force f.sub.p which is activated vertically to the moving direction of the movers 1 and 2 and is not contributed as the thrust force varies corresponding to the position X of the movers 1 and 2 as shown in FIG. 3. Referring to FIG. 3, when the center line of each magnetic pole of the permanent magnet 4 coincides with that of the tooth (projected portion) of the mover and the magnetic flux therebetween becomes maximum, the magnetic pull force becomes maximum without relating to the polarity of the permanent magnet 4. On the contrary, when the boundary 46 between the N pole and the S pole of the permanent magnet 4 coincides with the center line of the tooth (projected portion) of the mover and the leakage flux between the annexed poles of the permanent magnet 4 becomes maximum, the magnetic pull force becomes the smallest without relating to the polarity of the permanent magnet 4. As shown in FIG. 6, the magnetic pull force varies at each period T which corresponds to 1/2 of the pitches 2T of the tooth.
Since the magnetic pull force f.sub.p acts constantly to one direction, the force applied to the contacting portion (not shown) between the wheel attached to the movers and the stator is increased adding the weight of the movers to the magnetic pull force f.sub.p. Namely, the friction force corresponding to the friction coefficient at the contacting portion and the movement of the movers is disturbed.
The magnetic pull force f.sub.p is proportional to the volume of the magnetic flux at the air gap between the movers and the stator. When the volume of the magnetic flux at the air gap is increased, the magnetic pull force between the stator and the movers is increased. As a result, the friction force generated between the movers and the stator is increased, so that the acceleration corresponding to the generated thrust force can not be obtained, and the movers is not able to be moved in high speed.
Referring to FIGS. 2 and 3, the relationship between the magnetic pull force and the thrust force shows that the thrust force becomes the smallest when the magnetic pull force becomes the largest. Since the phase of the thrust force and the magnetic pull force between the movers 1 and 2 have delays 180.degree., respectively, when the magnetic pull force of the mover 1 is maximum and the thrust force thereof is minimum, the magnetic pull force of the mover 2 becomes minimum and the thrust force thereof becomes maximum. As a result, such a drawback is raised that the rotational force around the nonmagnetic material 8 connecting the movers 1 and 2, and the mover 2 is moved up and down in a vertical line.
In the above explanation, we explained in the case that the yoke provided with the permanent magnets is used for the stator and the magnetic poles wounded by the coils and having teeth are used for the movers. The problem explained above occurs in the case that the stator and the movers are replaced.
Further, the permanent magnet type linear motor of the prior art has a drawback in the magnetization of the small pitch permanent magnets arranged alternatively relating to the polarity of N pole and S pole on the stator as explained latter.
Hereunder, we will explain the magnetization of the permanent magnets of the linear pulse motor.
Referring to FIG. 1, the thrust force of the linear pulse motor is proportional to the variation of the linkage fluxes .PHI..sub.A and .PHI..sub.C of the stator coils 6 and 7 to the positional displacement of the stator yoke 3. For attaining high thrust force of the linear pulse motor, it is necessary that the tooth pitches of the stator A phase magnetic pole 1 and the stator B phase magnetic pole 2 and the magnetic pitch of the mover permanent magnets 4 are made small, and the linkage magnetic flux variation rate is made large. The miniaturization of the magnetic pole pitch of the mover permanent magnet 3 is necessary for attaining high thrust force.
However, the conventional permanent magnets 4 provided for the mover 3 are magnetized simply by N pole and S pole alternatively as shown in FIG. 4. According to the conventional permanent magnet type linear pulse motor shown in FIG. 4, when the magnetization pitch thereof is made small for increasing the thrust force of the motor, a drawback mentioned later is raised.
FIGS. 5 and 6 show main structure of the conventional magnetization apparatus 10 for magnetizing the surface of the permanent magnet material 14.
The magnetization apparatus 10 shown in FIG. 5 carries out the magnetization of the surface of the permanent magnetic material 14 by making the surface of the tip portion of the core 13 to a predetermined magnetization pitch. The magnetic flux generated from the tip portion 9 of the magnetization apparatus 10 passes through the permanent magnet material 14 as shown by the arrow. The thicker the permanent magnetic material 14, the weaker the magnetomotive force of the permanent magnetic material becomes. Since the permanent magnetic material 14 has to be magnetized by many poles having a small pitch, the magnetization apparatus 10 carries out the magnetization by moving the core 13 a predetermined pitch and converting the magnetic flux. At that time, since the present flux shown by the solid line passes through the former magnetized portion shown by the dotted line in FIG. 6, the magnetomotive force at the former magnetized portion is weakened. As apparent from the above explanation, when the permanent magnet material is magnetized a small pitch, the lowering of the magnetomotive force can not be avoided so that sufficient performance can not be obtained.
For preventing the above-mentioned drawback, it is suggested that the permanent magnetic material divided into small rectangular is magnetized, and the magnetized small rectangular permanent magnetic material is adhered to the mover in order to obtain a sheet of small magnetized permanent magnets.
Although this method mentioned above can magnetize the permanent magnetic material sufficiently, the manufacturing accuracy and fixing accuracy of the small permanent magnet is inferior to the conventional motor. Namely, when the small permanent magnetic materials are arranged on the mover, the pitches of the permanent magnets are not same, so that sufficient performance can not be obtained by the above-mentioned conventional method.
As explained above, the conventional method in this field cannot resolve two drawbacks as follows.
(1) The permanent magnet material can not be magnetized having a small pitch and a high magnetomotive force.
(2) The permanent magnet material can not be magnetized having a small pitch and high accuracy.
In the above explanation concerning FIG. 1, we explained in the case where a permanent magnet 4 is used for the mover 3, and A phase magnetic pole and B phase magnetic pole are used for the stators 1 and 2. The problems explained in (1) and (2) mentioned above occur also in the case that the stator and the movers are replaced.